This invention relates to electric lamps having an end which comprises an insulating member element secured by means of electrode-supply conductors and locked against rotation and lateral displacement with respect to the lamp.
In Great Britain Specification No. 816,229 and 646,553, there are disclosed electric lamps or discharge tubes having a base which comprises a metal shell having an insulating member of insulating material disposed on a surface thereof, for example, in a recess which supports terminal contacts or bi-pins that are connected in an electrical lamp, for example, a fluorescent lamp, and filling the space between the conductor pins and the recess. In such a lamp, the ends may be moldable, and the insulating member may be moldable or may be simply affixed to the metallic shell. The insulating members or contact-carrying plates are preferably located in a recess of the metal shell and may be of various shapes, for example, as described in Great Britain Patent Specification 646,553, wherein an insulating disc or contact-carrying plate fits into a circular annular recess, and as in Great Britain Patent Specification 816, 229 wherein the end comprises a metal shell provided with an in turned deformable flange defining an aperture and a disc of moldable insulating material disposed within the aperture. The insulating member plate or disc carries the contacts and is adapted to elastically take up shocks and transmit the same at a region of particular strength as a result of the annular recess, thus greatly reducing the risk of damaging the end.
In the lamp of Great Britain Patent Specification 646,553, the insulating member 12 is a disc molded into the metallic shell 11. In the lamp of Great Britain Patent Specification 816,229, the insulating member is a contact-carrying plate 8 and fits into a circular, annular recess or it may be octagonal in shape and fits into an octagonal annular recess. In both configurations, the insulating member is substantially the same size as the shell or recess.
In modern discharge lamps, a bi-pin insulating member as currently used, in, for example, fluorescent lamp bases, uses a relatively large amount of insulating material. As illustrated in FIGS. 3 and 5 herein, such an insulating member is primarily rectangular in shape with chamfered corners and has two small apertures for fixation of the contact pins. Such insulating members are normally formed of synthetic compounds such as phenolic resins or plastic molding compounds to which is added plasticizers, lubricants, accelerators, fillers, and the like and add to the cost of manufacture of the lamp. There is a continuing need for cost reduction in the lamp manufacturing process.
An object of the invention is to provide an end for an electric lamp that allows for cheaper and more efficient lamp manufacture without decreasing the shear strength of the insulating member.
This object and other objects of the invention are accomplished, according to a first embodiment of the invention in which an electric lamp is provided with an end having an annular recess which contains an insulating member which is secured to the lamp by means of at least two conductors which each extend from the lamp through an aperture in the insulating member, the insulating member and the annular recess being so shaped that the insulating member is held against rotation and lateral displacement with respect to the lamp, and wherein the insulating member comprises cut-out portions in an area remote from the ends thereof, and preferably in a central portion thereof, and most preferably in an area adjacent to the apertures, through which underlying material of said annular recess is exposed.
In a preferred embodiment of the invention, a discharge lamp, preferably a fluorescent lamp, is provided which comprises a metal end having an annular recess which contains an insulating member secured to the lamp by means of at least two conductor pins disposed in side-by-side relationship in the metal end, the annular recess having a substantially rectangular shape with rounded corners and the insulating member contained therein having two substantially octagonal portions connected by a portion in the shape of a parallelogram, each conductor pin extending from the lamp end through an aperture in an octagonal portion of the insulating member, said insulating member and said annular recess being so configured that the insulating member is held in the recess without rotation and lateral displacement with respect to the lamp.
The lamp end with annular recess is preferably formed of a metallic shell stamped out of copper, aluminum, iron or combinations thereof by methods well known in the art.
Similarly, the insulating member is preferably formed of materials well known in the art such as thermosetting resins, and particularly phenolic resins.
It has been found that the insulating members which comprise cut-out portions in an area remote from its ends as described herein may be manufactured without loss in shear strength when compared to prior art insulating members without the cut-out portions. It has also been found that the shear strength of the insulating members with cut-out portions may be further enhanced according to the invention when shear points that result from the cut-out portions are eliminated. This may be simply achieved, for example, by rounding out the sharp edges which constitute shear points of the cut-out portions.
Additionally, it has been found that substantial savings may be realized in the manufacturing process as a result of utilization of the invention. The insulating member can be manufactured by means known in the art, for example, by stamping the same from a sheet of suitable insulating material. The present invention permits a manufacturing process however that utilizes less material and that generates less waste and scrap material. For example, when utilizing an insulating member having the preferred configuration of a disc having double octagonal-shaped portions connected by a central rectangular-shaped portion as illustrated in FIGS. 2, 4 and 5 herein, the area of insulating material necessary to manufacture the insulating member is reduced by approximately 18% when compared to the area of insulating material necessary to manufacture an insulating member having the conventional rectangular configuration. The insulating member according to the present invention removes material from areas of the configuration while maintaining the required functionality of the conventional insulating member with all of its mechanical, electrical, and thermal characteristics. This allows for more efficient use of the raw material with less scrap and permits the manufacture of more insulating members from a standard size sheet of insulating material in an automated process with less hits and passes of the equipment.